Soft Imprinting: Creating Highly Ordered Porous Anodic Alumina Templates on Substrates for Nanofabrication

We demonstrate a “soft‐imprinting” method for the fabrication of highly ordered porous anodic alumina (HOPAA) templates on different substrates (such as Si, glass slides, and flexible polyimide films) over large areas (> 1.5 cm²). In this process, Ar plasma etching is employed to soft imprint an evaporated Al film on the substrates using a free‐standing HOPAA template as a mask, thus creating ordered nanoindentations on the Al surface. The ordered nanoindentations in turn guide the subsequent anodization of Al to generate HOPAA templates on the substrates (HOPAA–substrates), which inherit the pattern of the free‐standing HOPAA mask. This soft‐imprinting technique is also applicable to the fabrication of HOPAA on flexible polymer films. To demonstrate the potential uses of the HOPAA–substrates in nanofabrication, highly ordered Au nanowire arrays are fabricated on a Si substrate and TiO₂ nanotube arrays are prepared on a glass substrate via solution‐ and vapor‐based fabrication processes, respectively.     

一维磁纳米线阵列的制备及其应用

综述了以多孔阳极氧化铝为模板制备一维磁纳米线的方法,包括溶胶-凝胶法、化学沉积法和电化学沉积法等。阐述了一维磁纳米线在磁记录、巨磁电阻、量子磁盘及高密度存储等领域的应用前景。     

Long-range-ordered Ag nanodot arrays grown on GaAs substrate using nanoporous alumina mask

With more and more attention given to the plasmonic nanostructures enhancing light trapping of solar cells, the fabrication of metal nanostructures becomes more and more important. In this work, we fabricated porous anodic alumina on SiO₂/GaAs substrate and obtained periodic Ag nanodots with hemispherical shape by electron beam evaporation. During the experiments, it was found that the properties of barrier layers of porous anodic alumina fabricated on SiO₂/GaAs and SiO₂/Si substrates after pore-widening are different. The through-hole porous anodic alumina film on SiO₂/GaAs substrate cannot be obtained after a long pore-widening process. The additional Ar ion bombardment against the samples was needed in our experiments to get the through-hole porous anodic alumina films on SiO₂/GaAs substrate.     

Direct electrodeposition of highly ordered magnetic nickel nanowires on silicon wafer

Highly ordered nickel nanowire (50 and 12 nm in diameter) arrays were successfully deposited into the nanoporous alumina template film on a gold-coated silicon wafer. The electrodeposited nickel nanowires have a preferred (220) fibre texture, that is the [110] direction parallel to the wire axis. With electropolishing, nanoporous alumina template with ordered and uniform pores was prepared by anodisation. By complete removal of the barrier layer and careful control of electrodeposition procedures, nearly 100% pore filling of uniform nanowires can be directly deposited onto the Au-coated silicon substrate, therefore no pattern transfer is necessary and incorporation of these nanowires into silicon-based devices is readily possible     

Nanostructured layers of anodic aluminum oxide on insulating substrates

A method for creation of porous alumina layers on insulating substrates is proposed. The anodic oxidation of thin aluminum films is performed in two stages: formation of a thin dense oxide layer and its local breakdown followed by the final oxidation of the film with a propagation of the oxidation front from a breakdown region to periphery. Aluminum oxide layers exhibit quasi-ordered structure with the pore diameter ranging from 10 to 100 nm and depending on conditions of electrochemical oxidation. The method provides the aluminum film oxidation right to the insulating substrate (i.e., the absence of residual metal phase inclusions on the interface) and can be used for the creation of matrix and composite structures for semiconductor microelectronics.     

Template‐Assisted Synthesis of π‐Conjugated Molecular Organic Nanowires in the Sub‐100 nm Regime and Device Implications

π‐conjugated molecular organics such as rubrene, Alq₃, fullerene, and PCBM have been used extensively over the last few decades in numerous organic electronic devices, including solar cells, thin‐film transistors, and large‐area, low‐cost flexible displays. Rubrene and Alq₃, have emerged as promising platforms for spin‐based classical and quantum information processing, which has triggered significant research activity in the relatively new area of organic spintronics. Synthesis of these materials in a nanowire geometry, with feature sizes in the sub‐100 nm regime, is desirable as it often enhances device performance and is essential for development of high‐density molecular electronic devices. However, fabrication techniques that meet this stringent size constraint are still largely underdeveloped. Here, a novel, versatile, and reagentless method that enables growth of nanowire arrays of the above‐mentioned organics in the cylindrical nanopores of anodic aluminum oxide (AAO) templates is demonstrated. This method 1) allows synthesis of high‐density organic nanowire arrays on arbitrary substrates, 2) provides electrical access to the nanowire arrays, 3) offers tunability of the array geometry in a range overlapping with the relevant physical length scales of many organic devices, and 4) can potentially be extended to synthesize axially and radially heterostructured organic nanowires. Thus prepared nanowires are characterized extensively with an aim to identify their potential applications in diverse areas such as organic optoelectronics, photovoltaics, molecular nanoelectronics, and spintronics.     

用AAO为模板组装磁性金属Ni纳米线阵列

以多孔阳极氧化铝(AAO)为模板,采用直流电沉积的方法,制备了磁性金属Ni纳米线阵列。选用SEM、TEM、XRD等测试手段,对其微观形貌和结构进行了表征。结果表明:制得的Ni纳米线阵列排列规整、长度一致、直径与模板孔径基本一致,约为250nm,而且是结构紧密的多晶体。研究了电沉积时间对Ni纳米线长度的影响,发现电沉积时间应不超过15h。     

模板合成法制备ZnO纳米线的研究

在草酸和硫酸电解液中分别制备了孔径为40 nm和20 nm左右的多孔氧化铝模板,用直流电化学沉积的方法,在模板孔洞内电解沉积Zn,对其进行高温下的氧化,可得到高度有序的ZnO纳米线.扫描电子显微镜观察显示,多晶的Zn纳米线均匀地填充到多孔氧化铝六角排布的孔洞里,直径与模板孔径相当.X射线衍射谱测量证实,制备的Zn纳米线和ZnO纳米线均为多晶结构,并且对比了模板孔径对纳米线结构的影响.测量了多孔氧化铝厚膜和Zn/Al2O3组装体的吸收光谱,发现其在红外波段的吸收系数有逐渐降低的趋势.     

Single‐Crystal Organic Nanowire Electronics by Direct Printing from Molecular Solutions

A one‐step process to generate single‐crystal organic nanowire arrays using a direct printing method (liquid‐bridge‐mediated nanotransfer molding) that enables the simultaneous synthesis, alignment, and patterning of nanowires from molecular ink solutions is reported. Using this method, many single‐crystal organic nanowires can easily be synthesized by self‐assembly and crystallization of organic molecules within the nanoscale channels of molds, and these nanowires can then be directly transferred to specific positions on substrates to generate nanowire arrays by a direct printing process. The position of the nanowires on complex structures is easy to adjust, because the mold is movable on the substrates before the polar liquid layer, which acts as an adhesive lubricant, is dried. Repeated application of the direct printing process can be used to produce organic nanowire‐integrated electronics with two‐ or three‐dimensional complex structures on large‐area flexible substrates. This efficient manufacturing method is used to fabricate high‐performance organic nanowire field‐effect transistors that are integrated into device arrays, inverters, and phototransistors on flexible plastic substrates.     

直流电沉积法制备铁纳米线阵列及表征

为了制备结构规整的Fe纳米线阵列,以多孔阳极氧化铝(AAO)为模板,采用直流电沉积法制备了Fe纳米线阵列,并利用SEM、TEM、XRD等测试手段对其微观形貌和结构进行了表征。结果表明:所得的Fe纳米线阵列结构规整、直径与模板孔径基本一致,约为250nm,是结构紧密的多晶体。     

Arrays of Ordered Pb Nanowires and Their Optical Properties for Laminated Polarizers

A laminated micropolarizer of Pb nanowire arrays was fabricated within an anodic alumina membrane (AAM) by anodization of the pure Al foil and subsequent electrodeposition of Pb. X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, selected‐area electron diffraction, and high‐resolution electron microscopy investigations reveal that the ordered Pb nanowires are essentially single crystal, and have an average diameter of 40 nm. Spectrophotometry measurements show that the Pb nanowire arrays embedded in AAM can only transmit polarized light vertical to the wires. An extinction ratio of 17 to 18 dB and an average insertion loss of 0.4 dB cm^–1 in the wavelength range of 1 to 2.2 μm were obtained, respectively. Therefore, these Pb nanowire/AAM composites can be used as a wire grid type micropolarizer.     

Title: Using Alignment and 2D Network Simulations to Study Charge Transport Through Doped ZnO Nanowire Thin Film Electrodes

Factors affecting charge transport through ZnO nanowire mat films were studied by aligning ZnO nanowires on substrates and coupling experimental measurements with 2D nanowire network simulations. Gallium doped ZnO nanowires were aligned on thermally oxidized silicon wafer by shearing a nanowire dispersion in ethanol. Sheet resistances of nanowire thin films that had current flowing parallel to nanowire alignment direction were compared to thin films that had current flowing perpendicular to nanowire alignment direction. Perpendicular devices showed ～5 fold greater sheet resistance than parallel devices supporting the hypothesis that aligning nanowires would increase conductivity of ZnO nanowire electrodes. 2‐D nanowire network simulations of thin films showed that the device sheet resistance was dominated by inter‐wire contact resistance. For a given resistivity of ZnO nanowires, the thin film electrodes would have the lowest possible sheet resistance if the inter‐wire contact resistance was one order of magnitude lower than the single nanowire resistance. Simulations suggest that the conductivity of such thin film devices could be further enhanced by using longer nanowires.     

Study of the Piezoelectric Power Generation of ZnO Nanowire Arrays Grown by Different Methods

The piezoelectric power generation from ZnO nanowire arrays grown on different substrates using different methods is investigated. ZnO nanowires were grown on n‐SiC and n‐Si substrates using both the high‐temperature vapor liquid solid (VLS) and the low‐temperature aqueous chemical growth (ACG) methods. A conductive atomic force microscope (AFM) is used in contact mode to deflect the ZnO nanowire arrays. No substrate effect was observed but the growth method, crystal quality, density, length, and diameter (aspect ratio) of the nanowires are found to affect the piezoelectric behavior. During the AFM scanning in contact mode without biasing voltage, the ZnO nanowire arrays grown by the VLS method produced higher and larger output voltage signal of 35 mV compared to those grown by the ACG method, which produce smaller output voltage signal of only 5 mV. The finite element (FE) method was used to investigate the output voltage for different aspect ratio of the ZnO nanowires. From the FE results it was found that the output voltage increases as the aspect ratio increases and starts to decreases above an aspect ratio of 80 for ZnO nanowires.     

超薄阳极氧化铝模版的制备

采用二次阳极氧化铝的方法制备出厚度仅为509 nm超薄多孔阳极氧化铝模版,氧化铝模版上孔洞大小均匀.呈完美的六角分布,孔径为35 nm左右,孔间距约为100 nm.成功地将多孔阳极氧化铝模版转移到硅衬底上,并在磷酸溶液中通孔,使薄膜上小孔双向贯通.可以十分方便的利用该模版合成纳米点、纳米柱等纳米结构.     

硅基底电子束蒸发铝膜阳极氧化特性

研究了硅衬底上电子束蒸发铝膜 ,在 H2 SO4 水溶液中阳极氧化形成硅衬底多孔氧化铝复合结构的过程 .硅衬底电子束蒸发铝膜的阳极氧化过程主要由多孔氧化铝的生长、氧化铝生长向氧化硅生长的过渡和氧化硅生长三个阶段构成 .硅衬底多孔氧化铝复合结构的透射电子显微镜观察表明 ,在硅衬底上形成了垂直于硅表面的氧化铝纳米孔 ,而孔底可形成 Si O2 层 .有序结构多孔氧化铝的形成不依赖于铝膜的结晶状态 ,而是由阳极氧化过程的自组织作用所决定的 .实验表明将多孔氧化铝制备工艺移植到硅基衬底上直接形成硅基衬底多孔氧化铝复合结构是可行的     

Controlled Fabrication of Multitiered Three‐Dimensional Nanostructures in Porous Alumina

We present the fabrication of multitiered branched porous anodic alumina (PAA) substrates consisting of an array of pores branching into smaller pores in succeeding tiers. The tiered three‐dimensional structure is realized by sequentially stepping down the anodization potential while etching of the barrier layer is performed after each step. We establish the key processing parameters that define the tiered porous structure through systematically designed experiments. The characterization of the branched PAA structures reveals that, owing to constriction, the ratio of interpore distance to the anodization potential is smaller than that for pristine films. This ratio varies from 1.8 to 1.3 nm V^?1 depending on the size of the preceding pores and the succeeding tier anodization potential. Contact angle measurements show that the multitiered branched PAA structures exhibit a marked increased in hydrophilicity over two‐dimensional PAA films.     

铝阳极氧化基板制备过程对埋置型Ta-N薄膜电阻的影响

在铝阳极氧化多层基板内用RF反应溅射制备了埋置型Ta-N薄膜电阻,研究了铝阳极氧化过程对Ta-N薄膜电阻和显微结构的影响.实验结果表明:Ta-N薄膜受上层多孔氧化铝膜影响在表层形成了由Ta2O5和Ta-O-N组成的氧化物凸起绝缘层,氧化物凸起层厚度与氧化电压有关.底层Ta-N薄膜电阻率和电阻温度系数基本保持不变,表层氧化凸起使电阻稳定性增加.     

Nanoparticle Arrays on Surfaces Fabricated Using Anodic Alumina Films as Templates

High density nanoparticle arrays on surfaces have been created using a template‐assisted approach. Templates were produced by evaporating aluminum onto substrates and subsequently anodizing the aluminum to produce nanoporous alumina films. The resulting templates have a narrow distribution of pore sizes tunable from ～ 25 to ～ 70 nm. To demonstrate the flexibility of this approach for producing nanoparticle arrays on various substrates, templates have been fabricated on silicon oxide, silicon, and gold surfaces. In all cases, a final chemical etching step yielded pores that extended completely through the template to the underlying substrate. Because the templates remain in intimate contact with the substrate throughout processing, they may be used with either vacuum‐based or wet chemical deposition methods to direct the deposition of nanoparticles onto the underlying substrates. Here we have produced gold nanodot arrays using evaporation and gold nanorod arrays by electrodeposition. In each case, the diameter and height of the nanoparticles can be controlled using the confining dimensions of the templates, resulting in high density (～ 10¹⁰ cm^–2) arrays of nanoparticles over large areas (> 1 cm²).     

Long K‐Doped Titania and Titanate Nanowires on Ti Foil and FTO/Quartz Substrates for Solar‐Cell Applications

Potassium‐doped titania and titanate nanowires are fabricated by moisture‐assisted direct oxidation of titanium. The influence of the fabrication conditions on nanowire structure and morphology is investigated. It is shown that the presence of potassium is essential for nanowire formation, while the nanowire structure and morphology are strongly dependent on the fabrication temperature. The longest nanowires (ca. 10 μm) are obtained at 650 °C. At this substrate temperature, nanowires could be produced over a large substrate area both by oxidation of the Ti foil as well as by depositing a Ti film on the substrate (quartz or fluorine‐doped tin oxide (FTO)/quartz). Photovoltaic cells based on these nanowires are fabricated. The cell performance is dependent on the nanowire fabrication temperature and the substrate used, as well as on the annealing environment. Short‐circuit current densities of I_sc = 3.05 mA cm^–2 and I_sc = 4.97 mA cm^–2 could be obtained for Ti foil and FTO/quartz substrates, respectively, while the corresponding power‐conversion efficiencies are η = 0.93 % and η = 1.88 % (under AM 1.5 illumination, 100 mW cm^–2; AM: air mass).     

石墨烯上生长GaN纳米线

采用金属Ga升华法在石墨烯/蓝宝石衬底上生长了高质量GaN纳米线,研究了不同的生长条件,如NH3流量、反应时间、催化剂和缓冲层等对GaN纳米线形貌的影响,采用扫描电子显微镜(SEM)对GaN纳米线进行表征.研究发现,在适当的NH3流量且无催化剂时,衬底上可以生长出粗细均匀的GaN纳米线.反应时间为5 min时,纳米线密集分布在衬底上,表面光滑.在石墨烯/蓝宝石上预先低温生长GaN缓冲层,然后升温至1 100℃进行GaN纳米线生长,获得了具有择优取向的GaN纳米线结构.研究表明,石墨烯和缓冲层对获得GaN纳米线结构有序阵列具有重要的作用.